This invention is directed to apparatus for dropping expendable thermocouples into a BOF (Basic Oxygen Furnace) vessel, and more particularly, to apparatus capable of both storing and dropping thermocouples into the BOF at different selected times, as well as shearing off remaining electrical cables left behind from any expended thermocouples.
Free falling weighted thermocouple sensors are important control devices used in the production of steel in a BOF vessel. These weighted sensors provide low cost, reliable measurement systems that penetrate the slag layer and probe the steel bath to a sufficient depth to provide accurate temperature measurements via a cable that extends between the dropped sensor and recording equipment located in a BOF control room.
Access to the molten steel bath within a BOF is limited because a hood covers the mouth of the vessel during steelmaking operations. Therefore, it has become the practice to drop weighted sensors through the weigh hopper that is used to deliver flux into the steel bath. Weigh hoppers are located above the mouth of a BOF vessel located high above the operating floor of the steelmaking shop, and they usually include a flux chute that extends downward toward the vessel mouth. This location and physical arrangement makes weigh hoppers suitable for delivering the weighted sensors into the BOF. In the past, a steelworker was either stationed at the weigh hopper to toss sensors into the vessel whenever a temperature measurement was needed, or alternatively, he made repeated trips from the operating floor to the weigh hopper each time a sensor was dropped. In either event, such manual procedures are highly inefficient and a waste of manpower.
As a result, various past attempts have been made to provide automatic or semi-automatic storage and release mechanisms for delivering sensors into a BOF vessel. However, many of the past dropper devices worked poorly at best because the environment above the mouth of a BOF steelmaking vessel is extremely hostile to electro/mechanical equipment. For example, the ambient temperature above a BOF vessel is high enough to cause electrical equipment to fail. In addition, the fume and dirt emitted from the steelmaking vessel settles on any equipment brought into the area, and mechanisms such as air cylinders do not work well in this environment. Also, a fine graphite powder rich in carbon, called kish, falls as part of the fume and causes short circuiting in any exposed electrical connections.
Flames that erupt form the mouth of the vessel during oxygen blow operation can cause further problems for sensor equipment located above the BOF. It is common practice to drop sensors down the flux chute that extends toward the mouth of the BOF. The explosive flames can travel upward along structures such as the flux chute and cause damage to the sensor equipment positioned above.
And finally, a more recent problem that was discovered when automatic droppers were brought into use is the need to clear the sensor drop path of remaining electrical cables that are left behind from prior expended sensors that were dropped into the BOF. These remaining cables extend downward from the dropper apparatus, through the weigh hopper and along the flux chute, and dangle in a web like mass above the mouth of the vessel. The leftover cables create an obstacle to the free fall of following weighted sensors, and collisions with the dangling cables cause the sensors to enter the vessel erratically. This results in poor sensor penetration into the steel bath and unreliable temperature readings.
The various hostile conditions and problems that are described above have caused past sensor droppers to either fail or work poorly. One past sensor dropper is disclosed in U.S. Pat. No. 3,396,580 granted to Cole on Aug. 13, 1968. Cole discloses a dropper device comprising a plurality of spaced apart channel members for storing weighted thermocouples in a ready position above a BOF. In addition, Cole discloses a means to jettison remaining expended electrical cables before following sensors are dropped into the vessel. However, Cole uses air cylinders to position and release his sensors. We have found that the failure rate for air cylinders is quite high when they are exposed to the hostile environment found above the mouth of a BOF vessel. Knowing this, it then follows that the mechanics of the Cole dropper would most likely work poorly in this environment.
An even greater weakness of the Cole teaching is his need to drop two weighted devices into the BOF vessel each time a temperature measurement is taken. Cole shows a cone shaped secondary bomb attached to each temperature sensor that is dropped into the BOF. The cone shaped bomb supports the coiled electrical cable during the temperature probe, and following the temperature readings it is released and dropped into the vessel. As the secondary bomb falls from the dropper apparatus, it tears the expended "extension cord" free from its electrical connection and clears the drop path of expended cable before the next temperature sensor is dropped. As clearly shown in Cole's drawings, and as described in his specification, he uses alligator clips in order to provide a loose electrical connection that will insure the release of the extension cord. The ends of the extension cord are clamped in the alligator clips that extend from control panel wires.
Such connections are unreliable. They can generate a poor signal between the thermocouple and control panel, and they can be accidently disconnected during normal steelmaking operations, producing complete sensor failure.